The present invention relates in general to an apparatus for detecting leakage of fluids to the exterior from piping systems and instruments provided in the piping system. More particularly, the present invention relates to a fluid leakage detecting apparatus which is suited for detecting leakage of fluids over a very wide range in quantity of leakage from a very small quantity such as oozing to a large quantity in machines and instruments of power plants, pressure containers, petroleum pipe lines, petroleum tanks and hydraulic pumps, motors and various valves controlled by various fluids.
In plant equipment such as nuclear power plants, thermal power plants and others, piping systems for conveying fluids required for operations of the various equipment are densely laid on together with various machines and instruments attached thereto. In the long run of use or under external influences such as earthquakes, there will eventually be produced cracks, splits and interstices in the piping system and the accessories such as the valves and others and/or at various connections, resulting in that the fluids leak out through these cracks or interstices to endanger the safety in operation of the plant equipments. To deal with such problem, various detecting apparatus for detecting the leakage of fluid are proposed to be installed at locations where fluid leakage may be expected to occur. There are known many kinds of the fluid leakage detecting apparatus, e.g. sonic type, reflection type and electrical resistance type leakage detectors. However, those known detecting apparatus are generally complicated in structure due to their operation principles or configurations of their detector heads. Further, applications of these apparatus are generally limited to specific atmospheric or environmental conditions to which they are exposed. Thus, the known leakage detecting apparatus are not only expensive and voluminous but also lacking in the versatility.
In particular, the detecting apparatus of the above-mentioned types suffer from a limitation in the capability of detecting the fluid leakage depending on amount or quantity of the leakage. For example, it is difficult for the hitherto known detectors to detect with a reasonable reliability a very small leakage such as oozing. Further, since the prior art apparatus can detect the fluid leakage only when the fluid leakage has accumulated to a certain amount, it is impossible to detect the leakage immediately when the leakage occurs.
For example, in the case of the fluid leakage detecting apparatus of the sonic type in which when a fluid confined within a container leaks out through a fine opening such as a crack or split formed in the container, the sonic energy produced at the fluid leakage portion of the container is detected by a sonic sensor mounted to the container. Detection of the fluid leakage is often rendered very difficult, if not impossible, due to the background noise prevailing in the neighborhood. The fluid leakage detecting apparatus which is based on measurement of the reflection factor of the fluid in concern requires necessarily the use of optical means. Accordingly, high precision is required for the installation of this type detecting apparatus. Additionally, the apparatus is very expensive. For these reasons, the fluid leakage detecting apparatus of the reflection type is not suited, in most cases, for detecting fluid leakages in industrial machines. The detecting apparatus of the electrical resistance type is based on the principle that variation in resistance value of an electric resistance element brought about by contact with a leakage fluid to be monitored is detected. Examples of such electric resistance type fluid leakage detecting apparatus are disclosed in Japanese Patent Applications Laid-open Nos. 151250/80 and 113928/80. In the case of this type detecting apparatus, much consideration must be paid to the resistivity of the resistance element against chemical reaction as well as mechanical vibrations. Further, contact of a leakage fluid with the resistance element will not necessarily bring about immediate variation in the resistance value thereof to any substantial degree, when the fluid leakage is very small. In other words, the fluid leakage detecting apparatus of the resistance type is generally not satisfactory in respect of the response speed and the detecting sensitivity and thus is unsuited for the detection of minute fluid leakage.